Measuring bit geometry

Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 12:19 am

I've been toying with an idea for measuring bit geometry with out having to cut up a piece of wood for each new bit.

This is still a work in progress, but the preliminary attempt seems promising.

I'm using a cheap USB microscope, the software that came with it and a free image measurement app.

After taking detailed pictures of the bit (in this case a v-bit) I used the measurement app to check the included angle of the bit.

Measuring the width of the bit tip is a big pain using the microscope because you have to calibrate the image and magnification each time so I gave up on that and went old school. I held a block of wood with several feeler gauges next to the tip until I was satisfied I had the right size.

More experimentation and refinement of the process to follow.

Image 001.png
The yellow line was drawn to measure the included angle. In this case it measured 60.426

Image 002.png
Tip of bit with .020 feeler gauge. Pretty close.

Image 003.png
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby Martin Reid » Mon Aug 14, 2017 9:28 am

HighPockets..

Measuring bit geometry, now there's a subject close to my heart (some here would say "get a life"!).

Have you (or any other contributor) any ideas on accurately measuring 'three point' cutters like the one attached.

Sincerely and in good faith
Martin
Attachments
PCD_Turbo_Router.jpg
User avatar
Martin Reid
Vectric Apprentice
 
Posts: 38
Joined: Wed May 18, 2016 6:00 pm
Location: Lancashire UK
Model of CNC Machine: Shopbot

Re: Measuring bit geometry

Postby Leo » Mon Aug 14, 2017 1:25 pm

Martin Reid wrote:HighPockets..

Measuring bit geometry, now there's a subject close to my heart (some here would say "get a life"!).

Have you (or any other contributor) any ideas on accurately measuring 'three point' cutters like the one attached.

Sincerely and in good faith
Martin


Yes

In the machining industry there is a tool called a 3 point mike. It is a micrometer made to measure things like that. Generally the shank is the same as the cutter so a "regular" mike can measure the shank.

You could cut a slot in some dense hardwood and measure the slot.

You could mount the cutter in your spindle and set up an indicator to zero out on one side of the cutter, then zero out the axis on the DRO and move the spindle to indicator zero the other side of the cutter, reading will be on the DRO.
Imagine the Possibilities of a Creative mind

www.leosworkshop.com
User avatar
Leo
Vectric Wizard
 
Posts: 2418
Joined: Sat Jul 14, 2007 3:02 am
Location: East Freetown, Ma.
Model of CNC Machine: 1300 x 1300 x 254

Re: Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 2:55 pm

Sometimes problems need to be solved, even if there isn't a problem. :D :D
If I am doing cabinets then I'm happy with a 32nd of an inch accuracy. But if I'm cutting detailed models where a 32nd of an inch would wipe out a lot of detail then more information about the bit is required.
Bit geometry isn't important to everyone, but to some it is. And it's a fun distraction.
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby Mike-S » Mon Aug 14, 2017 3:02 pm

John, what a great idea.
Just tried with a 60 deg CMT Laser Point. Turns out it's only 49.5 deg--that's not even close.
I imported the pic right into Aspire and measured there.

Seems like this would be a good way to draw form tools, also.
Attachments
laserpoint60.jpg
User avatar
Mike-S
Vectric Wizard
 
Posts: 953
Joined: Mon Jun 13, 2011 6:45 am
Location: Hayesville, NC
Model of CNC Machine: Joe's Hybrid 4x4 (but 3x3)

Re: Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 3:12 pm

Mike, hadn't even thought about using it for form tools!
Great thought.
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 3:20 pm

Mike,

When you measure the bit make sure to rotate the bit until you find the widest point, then take the picture and measure. I had the same issue with a 30 deg bit.
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 3:22 pm

Also, once you find the widest point, rotating the bit 90deg will find the tip width
At least that's what I have found so far.
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby Mike-S » Mon Aug 14, 2017 3:32 pm

rotate the bit until you find the widest point

Yeah, did that--CMT was still way off.

A couple more:
A 40 deg engraving bit and a Sears 90 deg V-bit.

Good way to check the point quality too. Sears bit is missing it's point.
Attachments
40degengrave.jpg
90V.jpg
User avatar
Mike-S
Vectric Wizard
 
Posts: 953
Joined: Mon Jun 13, 2011 6:45 am
Location: Hayesville, NC
Model of CNC Machine: Joe's Hybrid 4x4 (but 3x3)

Re: Measuring bit geometry

Postby Mike-S » Mon Aug 14, 2017 3:47 pm

rotate the bit until you find the widest point

Well after thinking about this and Leo's comment, I may have given CMT a bum rap. It's a 3-flute, so the angle will be distorted under the microscope. 3-flute's not going to work this way. Measured with a protractor and it seems close to 55 or 56 deg. Still a little short of 60.
User avatar
Mike-S
Vectric Wizard
 
Posts: 953
Joined: Mon Jun 13, 2011 6:45 am
Location: Hayesville, NC
Model of CNC Machine: Joe's Hybrid 4x4 (but 3x3)

Re: Measuring bit geometry

Postby scottp55 » Mon Aug 14, 2017 4:31 pm

"I may have given CMT a bum rap."

Maybe not Mike....In Shopbot forum Gert took a bunch of VBits into the lab where he had access to an "Optical infa whatchamacallit" that's supposed to be dead nut on measuring bit angles, and warned me when I bought one that his CMT was 5.5(?) degrees shy of 60 degrees.
Still haven't tested it yet for waterline marks or even tweaked in feeds and speeds as I haven't needed the depth yet.
He said the cmt was the worst of the batch he tested:(
scott
User avatar
scottp55
Vectric Wizard
 
Posts: 2077
Joined: Thu May 09, 2013 11:30 am
Location: Kennebunkport, Maine, US
Model of CNC Machine: Shopbot Desktop 5.5"Z/spindle/VCP9

Re: Measuring bit geometry

Postby highpockets » Mon Aug 14, 2017 4:35 pm

Haven't tried a three or four fluted bit, should be able to measure half or one flute.
Will have to try.
John
Maker of Chips
User avatar
highpockets
Vectric Wizard
 
Posts: 1280
Joined: Tue Jan 06, 2015 4:04 pm
Model of CNC Machine: PDJ Pilot Pro

Re: Measuring bit geometry

Postby Leo » Mon Aug 14, 2017 5:30 pm

I find it hard to believe the CMT bits or any quality brand bits are that far off.

When measuring things from a "cast" shadow - there is distortion. Light refraction is horrible in these measurement processes.

I think you will find that if you rotate the cutter a little, you will get different readings. You would need to get the correct rotation orientation and the correct light aim and the correct alignment to be able to measure with any level of accuracy.

There is no way that I would call my CMT laser point 49.5 degrees. If that is true - CMT should be notified that their cutters are absolute TRASH and demand your money back.

Generally - standard manufacturing tolerancing on angles is about +/-30 minutes or 1/2 a degree. Even if the manufacturers tolerance was really really loose it would be +/- 1 degree. These things are made on CNC tool grinders like Huffman, or Walters and they cost 1/2 millions dollars or so. NO - I cannot believe that are off that much.

I don't even believe that the Chinese cutters are off that much.

Tomorrow, I will take my CMT laser cutters to work and measure them on my ST-Industries Optical Comparitor. Even so, I would call it a "reference" - not an absolute.
Imagine the Possibilities of a Creative mind

www.leosworkshop.com
User avatar
Leo
Vectric Wizard
 
Posts: 2418
Joined: Sat Jul 14, 2007 3:02 am
Location: East Freetown, Ma.
Model of CNC Machine: 1300 x 1300 x 254

Re: Measuring bit geometry

Postby Mike-S » Mon Aug 14, 2017 7:01 pm

Tomorrow, I will take my CMT laser cutters to work and measure them


Leo, if you have a 60 deg CMT, could you check that one? I love those bits, but it would be nice to know their true angle.
User avatar
Mike-S
Vectric Wizard
 
Posts: 953
Joined: Mon Jun 13, 2011 6:45 am
Location: Hayesville, NC
Model of CNC Machine: Joe's Hybrid 4x4 (but 3x3)

Re: Measuring bit geometry

Postby Leo » Mon Aug 14, 2017 7:03 pm

Mike,

If it is off anywhere near 5-10 degrees I am going to make a phone call to them.
Imagine the Possibilities of a Creative mind

www.leosworkshop.com
User avatar
Leo
Vectric Wizard
 
Posts: 2418
Joined: Sat Jul 14, 2007 3:02 am
Location: East Freetown, Ma.
Model of CNC Machine: 1300 x 1300 x 254

Next

Return to Hardware related questions

Who is online

Users browsing this forum: Gundawg and 2 guests